The -nopervasive switch simply does not load the Pervasive module
which is integrated in any executable ocaml normally produce... And
you're here using print_string which is in this module :)


Well, all the ways I know to output strings or whatever use Pervasive,
so I can't help you to replace it (I think even stdout is defined in
Pervasive~), but if you only want to get a small executable (let's say
you don't mind to return the int 42, instead of printing it), this
could help.